The present embodiments relate to spectrophotometer scanning systems particularly suitable for high speed online document color analysis. They are also applicable to item identification and characterization in many non-graphic arts applications ranging from paint industry color measurements to biotechnology applications such as performing DNA profiling. The embodiments also relate to defining a wide range spectra (visible, UV, infrared) for a particular media using a selected set of measured samples set by a tunable optical filter.
Spectroscopy is the measurement and analysis of electromagnetic radiation absorbed, scattered, or emitted by atoms, molecules, or other chemical or physical materials. Each object affects light in its own unique way. When light waves strike an object, the object's surface absorbs some of the spectrum's energy, while other parts of the spectrum are reflected back from the object. The modified light that is reflected from the object has an entirely new composition of wavelengths. Different surfaces containing various pigments, dyes, and inks (or chemistry/materials) generate different but unique wavelength compositions. Light can be modified by striking a reflective object such as paper; or by passing through a transmissive object such as film or a transparency. The pattern of wavelengths that leaves an object is the object's spectral data, which is often called the “finger print” of the object. Measuring spectral content of the object can give its intrinsic properties. For example, the region of the electromagnetic spectrum visible to the human eye ranges from about 400 nm to 700 nm, and if spectral measurements can be made in that wavelength range, then one can determine “the color of the object”. The amount of reflectance intensity decomposed at each wavelength is the most complete and infallible description of the color one can see. Hence in this case, the spectrophotometer becomes a true color sensor. If the UV-Vis spectrum (Ultraviolet and visible spectrum) is from 200 nm to 800 nm, then the UV-V spectrum could be used to identify the material composition—which is a form of non-contact, non-reactive chemical test—which can be used to analyze the compounds.
Spectrophotometers with a broad range of spectral synthesis have a wide range of application, including color printing, color measurements in displays, paints, textiles, electronic cameras, chemical analysis, environmental monitoring, measurement of bio-samples for medicine or personal identification, etc. All commercial spectrophotometers tend to be large in size with many optical elements.
Prior known full width array spectrophotometer systems utilized a linear array of photodetectors to detect an illuminated band of a test target, but required multiple different LED illumination sources of plural different color emissions in order to obtain an appropriate range of spectral response detections. In addition, such different color emissions had to be sequentially timed for emissive operation so the desired responses could be correspondingly distinguishably detected.
U.S. Pat. No. 6,295,130, issued Sep. 25, 2001, to Sun et al., entitled “Structure and Method for a Microelectromechanically Tunable Fabry-Perot Cavity Spectrophotometer”, discloses a measurement system for spot measurements requiring a single peak, which is generally difficult to achieve in Fabry-Perot devices. By “MEMS” it is meant “Micro-Electro-Mechanical-Systems” and by “Fabry-Perot cavity” it is meant an optical interference filter having a parallel glass plate silvered on the inner surfaces so that the incoming wave-is multiply reflected between them and ultimately transmitted. (cf. “MEMS: a New Joker in Microinstrumentation”, J. H. Correia et al., IEE Industrial Electronics Society Newsletter, January 2000; and, commonly assigned U.S. Pat. No. 6,249,346, issued Jun. 19, 2001 and entitled, “Monolithic Spectrophotometer”.)
Usually, scanner characterization is needed to transform scanned RGB values (scanner output signals) to colorimetric (i.e., visual) signals. Today's document scanners actually sense colors in terms of RGB coordinates, which approximate the human visual system. Most scanners are deviant from the human visual system in ways that differ depending on the media and ink being scanned. To address this problem, different characterizations, or profiles are built for different media. Creation of profiles for multiple material, media and image combinations results into loss of productivity. This can be easily fixed by having a wide area scanning spectrophotometer embedded on each printing device.
There is a need for an optical sensor that has the potential to measure colors at high printer speeds, at high resolution and with improved accuracy. A full width array optical sensing system, applicable for insitu measurements would provide significant advantages for automating publishing, production and decision processes in document production system via feedback through the proofing, prepress and creation stages. Such an optical sensor system would also have the capability for useful applicability for non-printing related applications, where materials or items can be identified through their color spectra.